1. Field of the Invention
The present invention relates to a semiconductor light emitting device formed by joining a semiconductor laser chip on a sub-mount in a junction-down manner, and more specifically to a semiconductor light emitting device that can reduce the polarizing angle of a laser, and a method for manufacturing such a semiconductor light emitting device.
2. Background Art
GaAs is used as a material of the substrate for a semiconductor laser, and Fe or highly heat-dissipating Cu is used as a material of the package for mounting the semiconductor laser. Here, the coefficient of linear expansion of GaAs is 6 (×10−6/° C.), the coefficient of linear expansion of Fe is 11 (×10−6/° C.), and the coefficient of linear expansion of Cu is 17 (×10−6/° C.). Therefore, when the semiconductor laser having a GaAs substrate is directly adhered to an Fe package with solder or the like, residual stress occurs due to difference in coefficients of linear expansion, and there is a case wherein the semiconductor laser is damaged. When a Cu package is used, the difference in coefficients of linear expansion becomes further significant, and residual stress becomes further significant.
Consequently, a sub-mount formed of AlN or the like is inserted between the package and the semiconductor laser. Here, AlN has a coefficient of linear expansion of 4 (×10−6/° C.), which is close to the coefficient of linear expansion of the GaAs substrate, and has a high mechanical strength. Therefore, by inserting the AlN sub-mount, the residual stress of the package is lowered.
However, even if the sub-mount is inserted, the residual stress applied to the semiconductor laser chip in the assembled state cannot be made zero. Therefore, conventionally, in order to lower the residual stress, the composition of solder used for joining or the material for the sub-mount was changed, the assembling conditions were adjusted, or the solder layer was thickened. Also in order to relax the stress in the vicinity of the light-emitting point, a structure wherein the laser chip is protruded from the sub-mount has been proposed (for example, refer to Patent Document 1).
[Patent Document 1] Japanese Patent Laid-Open No. 2001-156379